Although Birch himself claimed to have been born in New York, detective Edward Bonney alleged that Birch's father stated that Robert had been born in North Carolina. He had moved with his father and his two brothers to Illinois as a child. He became involved in crime as a teenager, being described by Bonney as "suspected of robbery and even of murder ever since he had attained the age of fifteen", and was considered a longtime member of the so-called Banditti of the Prairie. He was alleged by James Tevis of being involved in the torture and murder of George Davenport at his home on July 4, 1845. He was one of several members later identified by Edward Bonney who had infiltrated the gang as a counterfeiter. Birch was soon apprehended, in part to information from Bonney, and he soon agreed to testify against the others in exchange for a reduced sentence. Granville Young and brothers John and Aaron Long were later executed for the murder. After several court delays, Birch escaped from jail in Knoxville, Illinois on March 22, 1847.